Live streaming is not a novelty. Bambuser, Ustream, Livestream and a few more have been around for years now.
Still, since it´s launch in march 2015 Periscope seems to be the new new thing now. No, they are not alone, Meerkat was launched in February 2015 but Periscope seems to gather more attention. Why? Some say Periscope is just plain nice to use and others say it is because of Twitter.